docs: def read_files(*filenames):
      """
      Output the contents of one or more files to a single concatenated string.
      """
      output = []
      for filename in filenames:
          f = codecs.open(filename, encoding='utf-8')
          try:
              output.append(f.read())
          finally:
              f.close()
      return '\n\n'.join(output)